Not really "Unlimited"
I believe Karl got it wrong. Read through the complicated formulas and you'll see that more Wifi does not generate more cell minutes/data/txt.
The complicated "CUI" formula hides the fact that there is a "soft cap" of cellular use for all users. Yes, you can exceed it for a few months before getting booted off, but if you're a consistent heavy cell talk/data/txt users, you will get in trouble.
And, no, making a dummy Wifi call all night long won't magically replenish your "cell bucket". If your bucket is empty, the only thing you can do is cut back immediately on your cell usage, to bring your average cell usage in line with what they want you to use.
The overall business model is a sound and simple one: a Wifi centered phone service, with a cell phone backup. But their initial advertisements of "unlimited for $20!", while true in one aspect, won't work for someone who's looking to consume a lot of cellular data/txt/talk.
Yes, you're absolutely right. Their numbers are just based on using more wifi, so you get more total, not more cellular. The cellular is limited on it's own, and wifi doesn't count against anything.
This service is going to be great for kids, or people that want a smartphone, but don't have high usage patterns, or can deal with the limits and want better coverage at home.